1. Field of the Invention
This invention relates to fastening assemblies such as threaded inserts with anti-rotational locking devices used to receive threaded fasteners, more particularly, it relates to such assemblies having a non-circular anti-rotation locking plate used to secure the threaded insert.
2. Description of Related Art
The present invention relates to fasteners in general and more particularly to anchoring fasteners with lock rings that are preferably removably threaded in an anchoring structure and which typically cooperates with another fastener to hold other structures to the anchoring structure. Unscrewing of the threaded anchoring fastener is typically prevented by a circular locking ring having serrations around its periphery which is swaged into a suitably adapted recess in the anchoring structure. The threads of the insert and stud can be of hardened material, much harder than the anchoring structure. Examples of threaded anchoring fasteners are threaded inserts and studs.
Inserts installed in a workpiece provide a means of attachment of an object to the anchoring structure. Inserts are used when the stress requirements are greater than are provided by the anchoring structure. An insert can distribute the stress over a much greater area and can be harder material than would be provided by the anchoring structure alone. Inserts are also used to provide positive locking of the anchoring fastener in the anchoring structure by means of a locking device or feature contained within the insert. An example of an insert is a plug-like object having external threads to bit into or cooperate with the anchoring structure material. The insert also has internal threads for receiving the male threads of a cooperating piece.
Studs in contrast provide an anchor for attachment of objects to a anchoring structure. A stud secures to a anchoring structure with male threads and itself provides male threads for cooperation with a female threaded nut or other fastening means.
Threaded inserts of the type formed of a relatively hard material such an INCONEL 718 and adapted to be anchored in an anchoring structure of softer material such as aluminum have been widely used in such applications as gas turbine engine structures and similar structures. These threaded inserts typically are adapted to be threaded into a bore in the anchoring structure and then locked into position by means of a generally circular serrated locking ring which is adapted to mate with the threaded insert and to be forced into the surrounding anchoring structure such as by swaging. This causes cold flow of the anchoring structure material so as to secure the locking ring and thereby the insert against rotation in the anchoring structure. The serrations provide a means for allowing the forcing of the locking ring into the surrounding anchoring structure material by cold flow and also allow for relatively great torsional strength between the locking ring and the threaded insert. The cold flow of the anchoring structure material firmly secures the locking ring in position to prevent if rom becoming dislodged.
A major disadvantage of the serrated locking ring is that the serrations can result in unacceptable stress risers in he parent material and may become failure initiation sites and initiate failure in the anchoring structure if the parent material is highly loaded. Often the advantages of threaded inserts cannot be realized because the stress risers caused by the serrated locking ring is unacceptable. Furthermore, designs which propose to use keys or serrations that are preferentially oriented out of the primary stress field may result in failures if they are inadvertently installed in the wrong orientation or if the direction of the stress field changes.
Another drawback to these arrangements exists in that no practical, easily implemented technique is possible for removing an insert so as to allow replacement without damaging the surrounding material of the anchoring structure. The serrations of the locking ring on the new insert may not be firmly secured due to the presence of the old impressions left by the old locking ring of the original insert. Thus, drilling out of the old bore and replacement with a larger size insert would be necessary.
Therefore, the object of the present invention is to provide such an anti-rotational locking ring and threaded insert assembly which lowers stress risers caused by serrated edge locking rings and is easily removable thereby providing for easily replaceable threaded inserts.